1. Field of the Invention
The present invention relates to a construction machine, such as a hydraulic excavator, having an exhaust gas discharging structure.
2. Description of the Related Art
Ordinarily, a hydraulic excavator comprises an engine guard which covers, for example, an engine and a cooling fan, and has an exhaust opening or an opening for an exhaust gas in the top surface thereof for discharging exhaust gas. Noise cannot be prevented from leaking upward along with the exhaust gas discharged via the exhaust opening.
In an environment having high-rise apartment buildings near construction sites, in particular, the noise leaking upward from the hydraulic excavator causes noise problem to at least the residents living at higher floors.
The noise level of a hydraulic excavator is calculated by measuring sound pressure levels with a plurality of microphones disposed on an imaginary hemisphere face (parallelepiped face) so as to surround the hydraulic excavator and by calculating the total sound power emitted from the construction machine on the basis of the average of the sound pressure levels (dB).
The noise level measured in this way has a characteristic in that, if any one of the sound pressure levels is high, the average sound pressure level is also high. Therefore, in order to restrict the noise of the construction machine, it is necessary to reduce the noise of the entire construction machine.
In providing a soundproof design on the basis of exhaust gas flow, when the flow of air current from a cooling fan is made complicated, flow path resistance is increased, thereby reducing cooling efficiency. Therefore, it is necessary to restrict noise while maintaining smooth flow of air current from the fan.
A soundproof structure is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 4-55527. The sound-proof structure discharges exhaust gas downward from an exhaust opening of the machine body after cooling air current introduced from an intake opening at one side of the machine body in a widthwise direction has been guided to an engine cooling device disposed in a hood and the exhaust gas that has passed along the engine has been introduced into a duct path. The duct path is formed in an arcuate external wall of a counterweight.
In such a soundproof structure, however, since the flow of the cooling air current is guided to the duct path while changing the flow of the cooling air current in a complicated manner in the machine body, the flow path resistance increases, thereby increasing the load of the cooling fan.
In addition, since the duct path is formed at the counterweight, the space in the hood is reduced, thereby reducing the design freedom when disposing, for example, the engine.